The field of the invention is the display of anatomical images using data acquired from medical imaging systems, and particularly the display of three-dimensional anatomical images.
Medical and technical societies interested in imaging technology have historically advocated standardized image presentations. The intent is to assist the viewer in orienting objects (usually anatomy) in a consistent manner from one examination to another. Using these published recommendations for tomographic image presentation, for example, the examiner can assume certain spatial relationships based on the use of standard views. Out-of-plane or contiguous anatomic relationships can be inferred based on the presentation of a "standard" tomographic view.
To date, medical imaging documents have dealt primarily with tomographic (two-dimensional)images and have only begun to look at three-dimensional images. Conventional tomographic (e.g. CT, MRI and ultrasound) scans produce cross sectional views ("slices") that are viewed sequentially, and consequently one must imagine or extrapolate what the actual 3 dimensional anatomy should be. By using sophisticated algorithms and high performance computing, this cross sectional two-dimensional data may be rendered into three-dimensional (volumetric) representations of human anatomy. This type of imaging is becoming routinely used in such clinical applications as surgery simulation, radiotherapy planning, and quantification of tissue pathology. Specific anatomy data sets may also be obtained for realistic (virtual) endoscopic simulation. Technologies capable of higher dimensional digital imagery have concentrated on the more realistic presentation of anatomy and physiology and have not focused on how to navigate these new presentations.
The term virtual reality ("VR") refers to a human-computer interface that facilitates highly interactive control over a three dimensional scene of sufficient detail so as to evoke a response similar to that of a real scene. VR can provide natural access to a 3D data set by separating the user from the traditional computer interface and from physical realities, allowing the user to study a model, at any scale and at any orientation, without having to study the process required to generate or display that model. The ideal VR interface immerses the user into a computer generated environment that responds to human gestures and language with visual, tactile and auditory cues in real time. This interface maps the user's real world frame of reference on to that of the computer generated environment and must provide, at a minimum, some form of motion cues if the user is to successfully perform tasks within the virtual environment.
Virtual endoscopy ("VE") refers to a new method of diagnosis based on computer simulation of standard, minimally invasive endoscopic procedures using patient specific three-dimensional anatomic data sets. Examples of current endoscopic procedures include bronchoscopy, sinusoscopy, upper GI endoscopy, colonoscopy, cystoscopy, cardioscopy and urethroscopy. VE visualization of non-invasively obtained patient specific anatomic structures avoids the risks (perforation, infection, hemorrhage, etc.) associated with real endoscopy and provides the endoscopist with important information prior to performing an actual endoscopic examination. Such understanding can minimize procedural difficulties, decrease patient morbidity, enhance training, and foster a better understanding of therapeutic results.
Implementing VE on a VR display system allows simultaneous visualization of structure (virtual space) and orientation cues in a realistic manner. This form of VE provides for viewing control and options that are not possible with real endoscopy, such as direction and angle of view, scale of view, immediate translocation to new views, lighting and texture modifications and anatomic measurements. Additionally, VE provides access to many body regions not accessible to or compatible with invasive probes. Regions such as the heart, spinal canal, inner ear, biliary and pancreatic ducts and large blood vessels are important anatomic structures ideally suited for VE exploration.
An object presented in the digital domain of a computer has no inherent reference system to retain a meaningful relationship with the object and its origin. In virtual endoscopy, and other medical virtual reality and three-dimensional visualization applications, for example, anatomic localization and orientation is often lost due to the often complex mapping of the user's real world coordinate system to that of the computer-generated environment. Views bounded by the interior walls of an organ or other anatomic structure, alterations in image scale, instantaneous translocation of position and direction and non-standard or novel views can contribute to user disorientation. Once one enters the digital domain of a computer, orientation becomes essential in order to avoid the phenomenon of "lost-in-space". Once there are no tactile or visual aids to determine direction (i.e., up from down, right from left, near from far, etc.) there is a tendency to lose a sense of position, orientation and spatial relationships.
The only orientation currently utilized in medical imaging pertains to the relationship of the medical imaging device relative to the object being imaged. Acquired images are frequently referenced to acquisition aids. Examples are the designation of left and right on an x-ray film, angle of incidence on a fluoroscopic examination, and an angle of projection or acquisition on a tomographic image.
The use of spatial icons is extremely limited. An example of a current 3-dimensional spatial icon is one which shows a limited number of projected images and a cartoon or virtual human body roughly corresponding to the image projected. There is no dynamic interactivity between the image and the accompanying cartoon and in addition there are no numerical aids for precise orientation or reorientation.
Documents advocating image standardization all recognize that there are three tomographic planes corresponding to the three primary spatial planes of height, width, and length. However, to date no system has been devised which allows complete interactivity between an image and a spatial recognition system for the purpose of fostering standard presentation or spatial orientation.
Three-dimensional presentations, by their nature have no "standard" presentation. A "standard" presentation places unrealistic constraints on the examiner and would be perceived as limiting innovation. It is anticipated that higher dimensional images will have limitless interactivity analogous to our interaction with objects in our day-to-day environment. If this is considered ideal, then standard presentations will be impossible to implement. This being the case, there is considerable need for the observer to be spatially oriented to virtual images regardless of the interaction or presentation of the image.
A compounding problem with digital imagery is the ability to acquire multi-dimensional images utilizing multiple types of acquisition devices (i.e. ultrasound, computerized tomography, magnetic resonance, etc.). Today, most acquired images are oriented relative to the acquisition device. Because acquisition technologies do not contain knowledge of spatial relationships, the instrument cannot assist in the presentation of familiar or standardized views. In the environment of today's imaging devices, neither the machine nor the user are knowledgeable of orientation. Image orientation is based primarily on the nature of the acquisition device and not the organ or physiology in question. Ideally, the image should be presented in a consistent manner, emphasizing the object under study and not the particular medical imaging system that is used to acquire the image data.
With the introduction of 3-dimensional imagery, one has the ability to work within a virtual environment where objects can be dissected (cut into pieces), banked in a computer repository (stored), retrieved (re-assessed), and serially compared. After retrieval, the object can be reprocessed and reformatted to enhance understanding. It is also possible to replicate electronically acquired images as physical models (i.e. restoration of physical characteristics of the object referred to as "physical" or "model prototyping"). Although the potential for three-dimensional imagery appears unlimited, presently both the user and the acquisition device have no intuitive and effective spatial recognition aids to accomplish these essential functions.